Monday, March 9, 2015

Shady Business

As regular readers know, one of my minor obsessions is bicycle lighting and the many ways (in my curmudgeonly opinion) it could be improved. As a result, I was recently contacted by the inventor of the Sombra, dubbed "the world's first tail light diffuser."

If you're scratching your head over what a "tail light diffuser" might be, think of it as the bike equivalent of turning this:

... into this:

If you're looking at those photos and thinking, "But the first one is so much brighter! It has to be better!", then you haven't been paying attention and need to re-read the chapter on frickin' laser beams. I happen to be a firm believer that making lights brighter and tinier is not the be-all, end-all that the light makers would like you to think. My feeling (backed up by absolutely ZERO research) is that I'd rather have a lot of surface area lit up, and if I have to lose some retina-searing power to get there, I'm OK with that.

The Sombra is just that: More surface area for the light you already have. It's a very simple design, a translucent plastic shade that mounts over your existing taillight to give those around you more to see. I was given a review sample by the kind folk(s) at Sombra (BLOGGER FREE SCHWAG DISCLOSURE!), so I gave it a go on my daily driver.

Here's the titanium test-bed from the side with its normal rear illumination, a Planet Bike SuperFlash:

Same thing, with the Sombra installed:

The Sombra folks intend for it to be mounted on the seatpost binder bolt, wrapping over a seatpost-mounted light. However, since my light rides on the seatstay under my saddlebag, I improvised with my rack mounting points instead. The result's pretty much the same. As you can see, the side view doesn't give up much in the way of light intensity, but there's a lot more illuminated area to be seen. Major, major improvement.

So far, I'm on board. But I wish the Sombra folks had gone all-in and figured out a design that has the same effect on the rear view as well. Here's a look at the back of the bike sans Sombra:

And here it is with the Sombra installed:

Not a lot of difference, right? In fact, you have to look pretty closely to know that it's there.

I rode my normal commute with the Sombra installed for several weeks, but I can't say if drivers noticed me any more or less. Honestly, the drivers around here are (knock wood) pretty polite folks who don't give me a lot of reason to complain, so it wasn't much of a test. I
did find it a bit more challenging to turn my light on and off with the
Sombra installed while wearing bulky winter gloves, but not annoyingly
so. If any of my regular readers have a commute situation where they think a Sombra might make a bigger difference, I'd be glad to send you the prototype to try in your urban jungle if you promise to report back.

If anything, one of the Sombra's biggest strengths is paradoxically one of its biggest weak points. The thing is so simple, if you have the slightest DIY inclination, you're going to look at it and think, "I'll bet I could make that!" As soon as I started pondering ways to possibly reshape it to improve rear visibility, I realized that with a couple bucks' worth of plastic file folder and some scissors, I could probably hack any number of diffusers in whatever shape or size my twisted little mind could devise. Granted, the same response applies here as to the armchair modern art critic who says "my kid could paint that": Yes, but your kid didn't. The Sombra folks came up with this idea, did the hacking, worked the iterations, and deserve kudos for pushing the bike lighting business in the right direction. If they succeed -- or if the idea catches on -- we'll all be a little safer for it.

So, the verdict, in terrible bicycle magazine bullet point style...

PROS:

Definitely improves side visibility.

Easy to install.

Shouldn't be very expensive (final pricing isn't set yet).

CONS:

Doesn't improve rear visibility.

Can make it harder to turn your light on and off, depending on the light.

1 comment:

Anonymous
said...

I'll agree with the idea that the intensity of some lights can be excessive (and I'll include some car taillights in this group). By intensity, I'm thinking of the lumens per area. i.e. radiant flux density.

Diffusion is one way to reduce the intensity. I would argue that while it does achieve this goal, it does have the disadvantages of additional light loss and a wide radiation pattern that sends light in all directions instead of towards the people that you want to see the light.

Not everyone realizes that light is lost every time it hits a reflector or passes through optics. An opaque diffuser has significantly higher losses, though. You paid good money for those photons.... why pass them through a diffuser just to turn a lot of them into heat?

For the photons that do make it out of the diffuser, they will now be traveling in all directions. Unfortunately, the people around you are probably within 5 degrees of a horizontal plane. Out of the 180 vertical degrees that the light is radiating from the diffuser (i.e. from straight up to straight down), only photons within the 10 degrees closest to horizontal are reaching the eyes of the people around you. For every 1 photon hitting someone's eyes, 17 photons are lighting up the road or the sky. Certainly not the best arrangement.

A better method is to use multiple LEDs to create a more diffuse source of light, and for each LED to use optics to shape the light into a beam that serves your needs. There are LED optics that can produce a very wide beam that is also very tightly focused in the vertical axis. You might get up to half or more of your photons into the eyes of the people around you!

Now, obviously, this is going to be more complicated than throwing a diffuser around an existing light.

There used to be a really nice light from Cateye called the LD1100. It had 6 LEDs facing the rear, two facing left and two facing right. I've got one on my commuting 'bent, and it is good. It's a bit old tech and has been cancelled by Cateye.

I did see an interesting light at NAHBS, made by TRP, the brake folks. It wasn't directional, like most rear lights. It just shone (shined?) in all directions. I don't see it on their web site.. maybe it is still in development??